The sealing of the end area of the shoe shaft adjacent the outsole is particularly problematic for shoes especially waterproof shoes. This applies in particular to waterproof and breathable shoes the shafts of which are provided with an upper material, e.g., a textile or leather and a lining with a waterproof and water vapor permeable, i.e., breathable, functional layer.
Conventional lasting processes, wherein an insole is mounted to a last and an outsole-side end area of the shoe shaft is turned over a circumferential edge area of the insole and glued to the insole, require numerous production steps and cause problems when the lasting area is to be sealed. To make such lasted shoes, first the circumferential edge of the insole is covered with glue. The lasting is then effected in three zones and stages. First at the shoe tip, then at the side area, and finally the heel area is adhered. After each step, process time must elapse before the adhesive becomes sufficiently sticky. After the three stages, the adhesive is reactivated and thus softened in order to homogenize the transitions between the individual adhesive zones. This is intended to prevent insufficiently adhered spots at the zone interfaces through which water could penetrate.
Like other production processes, the lasting process is susceptible to the formation of water bridges at the outsole where the lining has a transition to the upper material. Since wrinkles caused by lasting often result in gaps in the adhesive through which water can penetrate, an adhesive layer is applied over the full surface after the lasting process in order to securely seal such wrinkles.
A laminate can be used as the waterproof, breathable, functional lining. This laminate lining comprises a liner, a foam-like plastic or a woven felt; a functional layer, preferably a membrane of stretched, microporous polytetrafluoroethylene (PTFE) and a backing fabric in the form of a textile reinforcement of the functional layer. In order to waterproofly bond the functional layer with an adhesive to the insole, the functional layer is laid open by a process known as skiving. During this process the liner and the foam are removed in this region. The foam affords a certain tolerance so that the liner can be removed from the functional layer without damaging it. It is only to allow for such a destruction-free stripping process that the entire lining laminate is provided with a foam layer. The necessity to cover the entire liner with a foam layer makes the lining laminate more expensive. Applying the adhesive, lasting zone by zone and covering the whole surface with adhesive to make the construction tight requires expensive manual work and long standstill times on the lasts. Therefore these process steps cause considerable production costs and the production throughput is so low that the number of shoes produced per unit of time does not fit into a mass production concept.
Such problems have been overcome by the process described in DE 3712901 C1 wherein a molding form is applied to the underside of the shoe shaft which has been lasted to the circumference of the insole. Said mold comprises a sealing lip arrangement which protrudes towards the lasted shaft area and which is shaped like the circumference of the insole. Through this injection mold liquid sealing material which hardens later is injected into the area limited by the sealing lip arrangement. During the lasting process an inner edge area of the lasted area is kept free from adhesive. The sealing material can thus seal this inner edge area of the lasted area when injected through the mold. This known injection molding process has proven to be suitable for producing waterproof shoes. However, the shoe manufacturer must make cost-intensive investments because he must buy a suitable injection machine.
It is basically state of the art to use an insole opening for injection of a curable material. U.S. Pat. No. 2,607,061 describes injection of adhesive into a central axial channel of a high heel to adhesively attach the heel to the shoe.
Frequently there is a need for a shoe with an impact-dampening padding material so that whenever the wearer's foot steps on the floor or ground while walking or running the impact caused by the steps are attenuated.